Question: What is your opinion of the fat substitute Oles-tra? I have read some negative things about this product and wondered if it would be good for you or not. Thank you.

Answer: Food manufacturers throughout the world have spent millions of dollars in an attempt to make some kind of fat substitute that would make fatty foods taste good without the problems associated with eating a high-fat diet.

According to an article in the U.S. Sports Academy's Sport Supplement (spring 1996), Proctor and Gamble spent the past 25 years trying to understand how the body digests fat. The original intent of the research was to determine if a fat could be developed that premature infants could digest more easily.

Fats belong to a class of compounds known as esters, which are made from acid molecules linked with an alcohol molecule (glycerol). The Proctor and Gamble biochemists discovered that if they attached more fatty acids to the alcohol molecule, it was easier to digest. They also discovered that once a sixth fatty acid was attached to a Swedish alcohol known as sorbitol, the compound became completely indigestible. This was the beginning of the development of Olestra.

The main problem with using sorbitol as the alcohol molecule for Olestra was the cost, so a sucrose molecule was substituted as a cheaper alternative. Combining the sucrose molecule with triglycerides (the most common type of fat in the diet) made the triglyceride indigestible because it was too large to pass through the mucous membrane of the small intestine. As a result, the compound (now called Olestra) is excreted as waste.

Even though Olestra passes through the intestines undigested, its effect in terms of taste and feel is identical to that of any oil. Since oils have a strong chemical affinity for the aromatic compounds that give them their taste and smell, oils extract these chemicals from the taste buds and allow the nose receptors to work normally. The idea was that you get the taste and feel of oil without the negative health effects of a high fat intake.

The downside of Olestra is that it can cause intestinal cramping, flatulence and loose bowels. It can also hinder the body from absorbing carotenoids, which are thought to reduce the risk of cancer. In addition, Olestra hinders the body's absorption of vitamins A, D, E and K.

One of the worst side effects is a condition researchers call "anal leakage." Some preliminary studies show that Olestra passes so rapidly through the intestines that it may leak through the anal sphincter in some people, a condition that would be socially embarrassing.

With the problems I have mentioned in terms of nutrition and leakage, I am going to be very careful choosing foods made with Olestra. It might be great for a few potato chips or some other snack food, but it would be better to change the overall diet to include more fruits and vegetables and lower the amount of animal products as the major way to a lower fat intake.